Modifying the shape and color of hair represents an important area of modern cosmetics. The consumer resorts to color-changing agents for fashionable hair style color schemes or for concealing gray or even white hair with fashionable or natural color tints.
For the provision of color-changing cosmetic agents, especially for the skin or keratin-containing fibers such as for example human hair, the person skilled in the art is aware of diverse systems according to the requirements of the dyeing or color modification.
The so-called oxidation dyes are used for long-lasting, intensive colorations with corresponding authentic characteristics. Such dyes usually comprise oxidation dye precursors, the “developer components” and “coupler components”. Under the influence of oxidizing agents or from atmospheric oxygen, the developer components form the actual colorants among each other or by coupling with one or more coupler components. The oxidation dyes are distinguished by intensive, outstanding, long-lasting coloration results. However, for colorations with a natural appearance, a mixture of a large number of oxidation dye precursors can be employed; in many cases, further substantive dyes are used for nuancing.
In spite of their advantageous coloration properties, oxidative hair dyeing agents present disadvantages for the user. In particular, some of the common oxidation dye precursors, among them p-phenylenediamine, are suspected to cause irritations for some consumers and thereby sensitizations or even trigger allergic reactions. Consequently, for these substances there is still need for improvement in their physiological acceptance profile. In the search for replacement substances, many compounds have been studied but which suffer from application related problems, especially the lack of gray coverage capability. Moreover, in spite of the highly developed dyeing systems, there still exists the need for dyeing systems that achieve excellent luminance and intensity of the colorations, concomitant, however, providing a very good durability and an excellent homogeneity.